Make synthetic analogs of the hypothalamic luteinizing hormone-releasing hormone (LH-RH) decapeptide in an attempt to obtain molecules which would block anterior pituitary receptors and inhibit their response to the hormone. The Contractor will prepare approximately thirty analogs of LH-RH giving highest priority to position two and three modification and secondarily to superactive agonist peptides, the structures of which can then be suitably modified to produce inhibitory peptides with higher binding affinity and biological stability. The peptides will be tested for in vitro and in vivo agonist and antagonist activity as well as for antiovulatory properties in small animals and LH-RH antagonism in primates.